1. Field
The present disclosure relates generally to light-emitting diode (LED) bulbs, and more particularly, to an LED bulb that uses quantum dots to produce a tightly controlled color distribution.
2. Description of the Related Art
Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs.
Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours.
While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements.
One approach to alleviating the heat problem of LED bulbs is to fill an LED bulb with a thermally-conductive liquid, to transfer heat from the LEDs to the bulb's shell. The heat may then be transferred from the shell out into the air surrounding the bulb.
Another drawback to an LED bulb is that LEDs tend to produce light that has a narrow emission band that may be centered at one end of the visible color spectrum. For example, one type of LED, based on gallium nitride (GaN), efficiently emits light over a relatively narrow emission profile centered at a peak wavelength in the blue region of the spectrum (approximately 450 nm). Gallium nitride LEDs are typically used because they can provide significantly brighter output light than other types of LEDs. However, the relatively narrow emission band, having a primarily blue color, may not produce the desired illumination qualities. For example, in some cases, it may be desirable that the LED provide a broader light emission spectrum that more closely resembles natural light. In other cases, it may be desirable that the LED provide a light emission that is precisely controlled to produce a tailored light emission spectrum.
Thus, it may be advantageous for an LED bulb to convert the narrow band of emitted wavelengths from an LED into a broader or specifically tailored light emission spectrum. To facilitate high-power operation, the light conversion technique should also be compatible with liquid-filled LED bulbs that use passive convection to maintain the temperature of the LED.